1. Technical Field
The present invention relates to a coating device and a coating method. More particularly, the present invention relates to a coating device and coating method in which, in a case in which a belt body is conveyed at high speed while a coating fluid with high viscosity is coated, liquid interruption due to entrained air that is carried in with the belt body does not occur.
2. Description of the Related Art
A planographic printing plate undergoes processes as follows to be fabricated. Commonly, at least one face of an aluminium web formed of pure aluminium or an aluminium alloy is dressed. Then an electrolytic oxidation layer is formed at that face as necessary, and thus a support web is formed. Next, a platemaking layer-forming liquid, such as a photosensitive layer formation solution, or a heat-sensitive layer formation solution, is coated onto a surface at the side of the support that has been dressed and is dried, and a photosensitive or heat-sensitive platemaking layer surface is formed.
Generally, a bar coater is employed for coating a coating liquid, such as a photosensitive layer formation solution, or a heat-sensitive layer formation solution, at a belt body, such as the aforementioned support web.
Conventionally, this bar coater is generally equipped with a bar and a coating section. While the bar is in contact with a lower surface of a continually running web, the bar rotates in a direction the same as the running direction of the web, or a direction opposite thereto. While the web is running, the coating section discharges the coating liquid at an upstream side from the bar, relative to the running direction of the web, and forms a coating liquid pool, thus coating the coating liquid onto the lower face of the web. The upstream side relative to the running direction of a web is hereafter referred to simply as “the upstream side”.
The bar coater may be an SLB-type bar coater or a PBS-type bar coater. An SLB-type bar coater disclosed in Utility Model Registration No. 2,054,836 includes a dam plate which is provided in proximity with a bar at the upstream side of the bar, and is formed such that thickness at an upper end portion thereof becomes thin toward a downstream side in the running direction of the web. The upper end portion of the dam plate curves toward the bar, and includes a flat face with a length of 0.1 to 1 mm at a peak portion thereof. A PBS-type bar coater disclosed in Japanese Patent Application Publication (JP-B) No. 58-004589 includes a first dam plate which is formed such that thickness at an upper end portion thereof becomes thinner toward a downstream side. This bar coater is also provided with a second dam plate at the downstream side of the bar. The downstream side in the running direction of a web is hereafter referred to simply as “the downstream side”.
However, when the running speed of the support web becomes higher, an entrained air layer, which is a film of air that follows along and runs with the support web, that is, entrained air, is formed at the surface of the support web.
In either of the above-described SLB-type bar coater and PBS-type bar coater, when an entrained air layer is formed at the surface of the support web, the entrained air layer is carried into the coating liquid pool. As a result, the coating liquid is not applied to the surface of the support web uniformly, and coating of the coating liquid is not carried out stably, causing film discontinuities.